PLC maintenance essentials and fault analysis

A, operating environment to ensure


Since the PLC for precision electronic products, automation and control system requires long uninterrupted run, thus PLC environment demanding, dust-proof, fireproof, waterproof, heat, lightning, electrical control room general arrangements have double glazing, install water cooling air-conditioning on the second floor, electronic room temperature control in 28 degrees; Dust is the PLC is installed in the 1M*2.2M*0.6M front panel glass door with lock in the control cabinet, the cabinet departments are installing the dust cover for cabinet cooling ventilation system.


Second, do the daily work


1, daily preparations: first familiar with the process, followed by descriptions of the PLC module information familiar, site layout understanding again, and finally make sure you had all kinds of testing tools to be in good condition.


2, and daily points check work: regularly for CPU of battery of voltage detection, are often situation Xia for 3V, regularly on constitute PLC system of related equipment of points check and maintenance, as UPS regularly maintenance, using downtime timing, on PLC the control cabinet for artificial dust, and cooling, PLC program of regularly artificial backup and battery backup and the the related bad devices of replaced, work.


Fault diagnosis of three, PLC


(A) General principles:


Fault detection method for PLC system: one, two, three, four smell touch hear, fivetrack pursuit, six replaced law.


A touch, check CPU of temperature high not high, CPU normal run temperature not over 60 ℃, for hand can accept of temperature for human temperature 37~38℃, feel suitable; II see, see the Board Shang of the module led whether normal; three smell, smell have odor, electronic components or line cable has no burned; four listening to, listening to has is moving, Luo silk nail loose, and following electrical normal work or not, listening to site staff of reflect situation; five appeared fault according to drawings and process to looking for fault location; Six pairs of uncertain parts replacement parts to determine the fault.


(B) concrete steps:


When the PLC software not functioning correctly, mainly to see the CPU RUN correctly, download the program again after the CPU is not properly cleared.


When the PLC hardware does not work correctly when the work is checked in the following order:


1, and view PLC power whether has electric: has electric is measurement voltage whether in +24V of ± 5% range within, has electric and normal, is for next; has electric not normal is for power module of output end and entered end for detection, if output end not normal and entered end normal, is replaced module; if entered end not normal, is for entered end of upstream law for corresponding check, as for 24V make DC transformer of entered voltage end of Exchange voltage 220V of ± 10% check, normal, Then replace the DC 24V transformer. No electric is by track pursuit, with principle figure + site layout total figure + wiring drawings, check to power module power of various electrical devices of output end of wiring whether right, not right, again wiring; right with multimeter is check air switch of into line end and outlet end has no normal power, no normal power, identified is outside also is itself reasons, if for outside is is voltage insufficient also is fundamental no voltage, or load overweight, and or serious had flow and so on of analysis, has been to will accident excluded normal power weizhi; If bad replace for itself.


2, understanding the CPU mode and priority: high priority STOP, HOLDUP, STARTUP (WARMRESTART, and COLDRESTART); lowerpriority: RUN, and RUN-P (PG/PC online reading and writing programs). View the CPU is in RUN mode or STOP mode, Flash or RUN mode and STOP mode and hold mode or debugging mode. If you only RUN mode the CPU and the Board is normally the 3rd step. If it is to keep the model, breakpoints with user program may be running in the debugger, or breakpoints appear in start mode, this refit program, control program can be downloaded to the CPU the Chinese side once again.


If STOP mode STOP caused by Visual Analysis: a, without electricity, analysis of causes, because the electricity sector problems, or abnormal power off (for 1K3AH UPS guarantee seldom goes away), usually for maintenance, maintenance after the end of the manual transmission. Using PLC online function converts the CPU mode from STOP to RUN; B, CPU, replace with new version of good with the same type of CPU; C, the Board is broken, ordered the Board replaced. Note to hardware replacement use original devices of the same product and the same model, the same version, or it will cause the actual PLC configuration and corresponding programming software hardware configuration hardware configuration in the database and cannot execute users control the normal cycle.


3 make all communication cables on the motherboard and expansion board inspection and prosecution of the module LED lights, see if there‘s a bad module fault light is on, if the module is not normal. For digital volume output module Shang the points actually and reality life Shang of electric switch is as of function and for often open points, so online maintenance the module of any is Shi, as long as in no wiring Shi and the address in program not to output signal Shi to detection its pass not pass on can has, if pass, is the points not normal, not General normal; not normal Shi to for hardware connection line of another points heavy received work; addition we also can with new module for replaced Hou, on replaced down of module of points for measurement pass broken state, pass, is the points bad , Do not pass this point as well. For digital input module points when Yu Dao-way coil is normally off, it can be online or offline detection table detect if pixel is not justifiable for the State, then some wiring; good for the State. As long as the hardware connection again after using the programming software the software is 0X or 1X address replacement. For analog input module is identical to the digital input module, each channel is equivalent to a wire form, that is equivalent to the normally closed, so detection method for measuring a table of channel switching capabilities to detect, when the State, as well, as bad off State channel; detection method of analog output modules digital output module with the same. If the bad channel hardware connection needs to be replaced channel and replaced with 3X or 4X addresses in the program; in addition to analog module to make selected checks of a range block, fuse is disconnected check, and so on. Software configuration is normal, generally current or voltage 1~5V 4~20mA, depending on the sensor and intelligence types to choose from. Hardware or channel replaced conditions of work permits is to STOP PLC CPU, then download the program again, if conditions do not allow the direct update changes to download program and keeps CPU. Good channel/input module but are not good and the last one have been using a channel/better series or special settings in the software.


4, and on large output module of Board Shang of power module in normal production State Shi is cannot power of, because at power words, will makes following electrical cabinet in the of often open following electrical into often open State, easy occurred errors, so to on this class of output module for detection Shi, to and site operation personnel for contact, for the part related equipment for manual operation Hou, again withdrawal to digital volume output module of power line Hou on module measuring points work.


5, the detection of various types of switches: such as relays, proximity switches, air switches and other devices work, is based on the type of switch is normally closed or normally open separate table to detect the barrier with the sense of status, its status and better devices instead, then the device is broken, replace it. For the circuit using normally open, they are used for manual control or automatic control currents of connected and disconnected; for a normally closed type is mainly used in the protection circuit. This know switch and protection class the normal state of the device on how to properly identify device is good or bad.


6, newsletter module detection is to use the simple use of the new communication module replacement module that is in use on the identification plate is normal.


7, measurement of a wire: wire by detecting breaking methods. Can use the known sense wire to detect wires do not know whether good or bad, are good conductors connected with the unknown conductor after the switching State.


8, of resistance testing: detection voltage charged when, without an electrical test when the corresponding resistance.


Four, the summary


Through testing, you can exclude most of the faults in the work, because the work involves AC single phase electric 220V and 24V DC operation of intersection, pay attention to safe knowledge accumulated while working with common sense, as well as safety precautions at work and gas safety regulations to ensure safe operation.

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